It is known to mount a yaw rate sensor on a rotatable body in order to measure a yaw rate of a rotary motion of the body. Known yaw rate sensors usually have a substrate on which one or multiple electrodes is/are situated. In addition, one or multiple detection masses is/are suspended on the substrate in such a way that the detection masses are located above the electrodes. The detection masses are suspended in the manner of a trampoline, so to speak. The detection masses are usually made of a solid material. When the detection mass or the detection masses is/are then excited to a vibration parallel to the substrate plane with the aid of a drive, a rotation about an axis which is in the substrate plane and is situated orthogonally with respect to the vibration direction of the detection masses, results in a deflection of the detection masses perpendicular to the substrate plane due to the Coriolis force. Consequently, the distance between the electrodes and the detection masses also changes. In this regard, the corresponding capacitance also changes. This change may be detected and converted into an appropriate yaw rate of the rotary motion of the body. The deflection of a detection mass is proportional to the Coriolis force acting on the detection mass. Yaw rate sensors in which the detection masses move out of the substrate plane when a Coriolis force is present may also be referred to as out-of-plane yaw rate sensors.
The above yaw rate sensors are generally acted upon by electrical voltages via the electrodes, in particular for electrostatic regenerative feedback; i.e., in fully resonant operation the detection mode is reduced to the frequency of the drive mode in order to increase the signal-to-noise ratio, and to compensate for the quadrature, i.e., the mechanical and/or electrical crosstalk of the drive motion in the detection path of the sensor element.
For applications in the automotive field, for example in electronic stability program (ESP) systems, for rollover sensing, or also in navigation systems, it is necessary to increase operating frequency fa of the yaw rate sensor to 15 kHz or even to 20 kHz to 40 kHz, since at these high frequencies interfering vibrations hardly ever occur in the automobile, and the yaw rate sensor therefore has a very high level of robustness with respect to interfering excitations. However, the increase in the operating frequency is accompanied by an increase in mechanical spring stiffness k of the yaw rate sensor. On the other hand, since for a yaw rate sensor which detects out-of-plane, electrode surface areas for the regenerative feedback and quadrature compensation effects do not increase in the same proportion as the spring stiffness, for the same applied voltages this results in a reduced regenerative feedback capability, i.e., the reduction in the detection frequency divided by the square of the regenerative feedback voltage, or a reduced quadrature compensation capability, i.e., the compensated quadrature divided by the square of the compensation voltage. This may result in considerable yield losses, since it is no longer possible for all production fluctuations, which result in variations in the necessary regenerative feedback and quadrature compensation effects, to be compensated for via the voltage level which is available in the evaluation circuit.
One option for preventing spring stiffness k of the yaw rate sensor from increasing despite a higher operating frequency fa is to reduce mass m of the detection masses, since fa=(k/m)1/2/2π. However, for sensors according to the related art, whose detection masses are structured from a single micromechanical layer, or for detection masses made of a solid material, a reduction in mass is accompanied by a reduction in the available electrode surface areas. Thus, the ratio of electrode surface area to mechanical stiffness, and thus also the regenerative feedback and quadrature compensation capability, is not improved as a result.
The known yaw rate sensors also have the disadvantage that in addition to their useful modes, i.e., the drive mode and the detection mode, they have additional vibration modes, so-called spurious modes. When such spurious modes are excited via electrical or mechanical disturbances during operation of the yaw rate sensor, false signals may appear in the output signal.